The present invention relates to variable displacement compressors that are employed in air-conditioning systems for automotive vehicles. More particularly, the present invention pertains to a variable displacment compressor that employs an inclinable cam plate to adjust displacement.
A clutchless-type variable displacement compressor is shown in FIGS. 10 to 12. As shown in these drawings, a housing 105 houses cylinder bores 101, a crank chamber 102, a suction chamber 103, and a discharge chamber 104. A drive shaft 107 extending through the crank chamber 102 is rotatably supported in the housing 105. A rotor 108 is fixed to the drive shaft 107 in the crank chamber 102. A swash plate 109 is accommodated in the crank chamber 102. The swash plate 109 is supported by the drive shaft 107 in a manner such that it is slidable and inclinable with respect to the drive shaft 107. Pistons 106 are coupled to the swash plate 109. Support arms 111 extend from the rotor 108 while associated guide pins 112 project from the swash plate 109. The support arms 111 and the guide pins 112 constitute a hinge mechanism 110. Each guide pin 112 has a spherical portion 112a, which is slidably fitted into a guide bore 111a extending through the associated support arm 111.
Accordingly, the swash plate 109 rotates integrally with the drive shaft 107. During the rotation, the hinge mechanism 110 enables the swash plate 109 to move between a maximum inclination position and a minimum inclination position while sliding on the drive shaft 107. As shown in the enlarged view of FIG. 11(b), a slight clearance is provided between the wall of the guide bore 111a and the associated sperical portion 112a in the hinge mechanism 110. The clearance permits smooth movement of the swash plate 109.
A pressurizing passage 113 connects the discharge chamber 104 with the crank chamber 102, while a conduit 114 connects the crank chamber 103 with the suction chamber 103. A displacement control valve 115 is arranged in the pressurizing passage 113. The control valve 115 adjusts the opening amount of the pressurizing passage 113 to alter the amount of refrigerant gas sent from the discharge chamber 104 to the crank chamber 102. This, in turn, adjusts the pressure in the crank chamber 102 in correspondence with the amount of refrigerant gas released through the conduit 114. The difference between the pressures acting on each side of the pistons 106, that is, the difference between the pressure in the crank chamber 102 and the pressure in the cylinder bores 101, is thus changed. As a result, the swash plate 109 is moved between the maximum inclination position and the minimum inclination position. This alters the stroke of each piston 106 and varies the displacement.
A projection 109a projects from the inner rear surface of the swash plate 109. A shutter 121 is arranged to abut against the projection 109a by way of a thrust bearing 122. As the swash plate 109 slides toward the minimum inclination position, the projection 109a and the thrust bearing 122 push the shutter 121. When the swash plate 109 is arranged at the minimum inclination position, a shutting surface 123, which is defined on the shutter 121, abuts against a positioning surface 124, which is defined on the corresponding inner wall of the housing 105. This disconnects the suction chamber 103 from a suction passage 125, which is connected to an external refrigerant circuit. In other words, when the shutter 121 disconnects the suction chamber 103 from the suction passage 125, the abutment between the shutting surface 123 and the positioning surface 124 restricts further sliding of the swash plate 109. In this state, the swash plate 109 is located at the minimum inclination position.
When the shutter 121 blocks the flow of refrigerant gas, the circulation of refrigerant gas through the external refrigerant circuit is impeded. This is advantageous in that the operation of the compressor, or rotation of the drive shaft 107, is continued even when cooling is not required. This structure eliminates the need for a costly and heavy clutch, which would be arranged between the drive shaft 107 and a vehicle engine 126. Consequently, the elimination of the clutch prevents shocks that would be produced when actuating or de-actuating the clutch.
A first spring 116, which is a coil spring, is located between the rotor 108 and the swash plate 109 on the drive shaft 107 to urge the swash plate 109 toward the minimum inclination position. Therefore, if operation of the compressor is stopped when the engine 126 is stopped and the pressure in the compressor thus becomes uniform, the first spring 116 sustains the swash plate 109 at the minimum inclination position. As a result, when the compressor commences operation, the displacement is minimum. In such a state, the torque load required for operating the compressor is minimum. Thus, the shock produced when starting operation is effectively suppressed.
A top dead center (TDC) portion 109b, which arranges each piston 106 at its top dead center position, and a bottom dead center (BDC) portion 109c, which arranges each piston 106 at its bottom dead center position, are defined on the swash plate 109. The piston 106 illustrated in FIG. 10 is arranged at the top dead center position by the TDC portion 109b. The BDC position 109c is shown on the opposite side of the drive shaft 107 in the drawing.
Two planes 117, 118 are defined on the central front of the swash plate 109, which is the surface facing the first spring 116. The first plane 117 extends from the TDC portion 109b toward the center of the swash plate 109. The second plane 118 extends from the BDC portion 109c toward the center of the swash plate 109. The first and second planes 117, 118 are inclined so that they become closer to the rotor 108 at positions closer to the intersection between the two planes 117, 118, or the ridge line K11.
The first spring 116 abuts against the swash plate 109 along the ridge line K11 between the planes 117, 118 when the swash plate 109 is located at the minimum inclination position. In this state, the swash plate 109 abuts against the thrust bearing 122. A line T is defined between the swash plate 109 and the thrust bearing 122. The swash plate 109 pivots about line T when inclining toward the minimum inclination position. The line T is included in a hypothetical plane H (FIG. 12), which extends parallel to the axis L of the drive shaft 107. As shown in FIGS. 11(a), 11(b), and 12, when the swash plate 109 is located at the minimum inclination position, the ridge line K11 is located at a position closer to the TDC portion 109b than the line T. More specifically, the ridge line K11 is located at a position closer to the TDC portion-109b than the hypothetical plane H.
Accordingly, when the swash plate 109 is located at the minimum inclination position, the first spring 116 presses the TDC portion 109b of the swash plate 109 and produces an inclining moment M11 that acts about the line T in a direction increasing the inclination of the swash plate 109. The clearance between the wall of the guide bore 111a and the associated spherical portion 112a in the hinge mechanism 110 permits a slight inclination of the swash plate 109 when located at the minimum inclination position. Consequentially, when the operation of the compressor is stopped, each spherical portion 112a is pressed against the swash plate side of the wall of the associated guide bore 111a (toward the right as viewed in the drawing). Therefore, the minimum inclination position of the swash plate 109 is so determined when the compressor is not operating.
However, during operation of the compressor, when each piston 106 approaches its top dead center position, a compression reaction is produced. The compression reaction acts on the swash plate 109 and forms an inclining moment M12 that acts about the line T in a direction decreasing the inclination of the swash plate 109. The inclining moment M12 is greater than the inclining moment M11, which is produced by the first spring 116. Accordingly, when the compressor is operated, each spherical portion 112a is pressed against the rotor side of the wall of the associated guide bore 111a. Thus, the direction each spherical portion 112a is pressed toward when the compressor is in operation is opposite the direction of that when the compressor is not in operation. Hence, the minimum inclination position of the swash plate 109 is so determined when the compressor is operating.
In other words, in the prior art compressor, the minimum inclination position of the swash plate 109 differs when the compressor is operating from when the compressor stops operation. The angle of the swash plate 109 at the minimum inclination position is determined during assembly of the compressor. However, when the compressor commences operation, the minimum inclination position of the swash plate 109 is displaced from the determined angle. This displacement must be taken into consideration when installing the swash plate 109. As a result, burdensome installation steps must be taken.